Process of using storable propellant fuels in supersonic combustion ramjets

ABSTRACT

Liquid propellant fuels such as liquid hydrazines, amine fuels, and blends thereof with hydrocarbons used as storable fuels for supersonic combustion in ramjets. The storable liquid fuel is decomposed in flight into a hot hydrogen-containing gas which is then injected into a supersonic air stream and subsequently oxidized in a supersonic combustion mode.

United States Patent [191 Wharton et al.

PROCESS OF USING STORABLE PROPELLANT FUELS IN SUPERSONlC COMBUSTION RAMJETS Inventors: Walter W. Wharton; Joseph W.

Connaughton, both of Huntsville, Ala.

Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

Filed: Oct. 6, 1967 Appl. No.: 674,064

US. Cl 60/207, 60/208, 60/209, 60/217, 60/218, 60/219, 149/36 Int. Cl. C06d 5/08, C06d 5/04 Field of Search 60/206, 207, 208, 209, 60/218, 219

SUPERSONIC AIR [451 May21, 1974 [5 6] References Cited UNITED STATES PATENTS 3,230,701 1/1966 Mullen et a1 60/207 Primary Examiner-Benjamin R. Padgett Attorney, Agent, or FirmEdward J. Kelly; Herbert Ber]; James T. Deaton [57] 7 ABSTRACT Liquid propellant fuels such as liquid hydrazines, amine fuels, and blends thereof with hydrocarbons used as storable fuels for supersonic combustion in ramjets. The storable liquid fuel is decomposed in flight into a hot hydrogen-containing gas which is then injected into a supersonic air stream and subsequently oxidized in a supersonic combustion mode.

6 Claims, 2 Drawing Figures EXHAUST PATENTED 21 h'ron, RS.

H 55 km m3 QzowmEnw .5225 mwNxo INVENT% Hm M Walter W Wharton Joseph W. Connou BY Mn? PROCESS OF USING STORABLE PROPELLANT FUELS IN SUPERSONIC COMBUSTION RAMJETS DEDICATORY CLAUSE The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

BACKGROUND OF THE INVENTION This invention relates to storable liquid propellant fuels, and in particular to a class of storable liquid fuels and a method of injection thereof for use in supersonic combustion ramjets.

In the operation of conventional ramjet engines used for propelling a vehicle such as a missile at supersonic flight speeds, the free-stream air flowing toward the engine at supersonic speeds is decelerated by a supersonic diffuser to approximately unity Mach number at the entrance to a subsonic diffuser. In the subsonic diffuser, the air is further diffused so that it arrives at the entrance of a combustion chamber, after having been mixed with a fuel in a mixing area or chamber to produce an air-fuel mixture stream, with a Mach number of approximately 0.2, but certainly less than unity. In the combustion chamber the fuel, generally a liquid hydrocarbon, is burned in the air. The hot gases are then discharged to the atmosphere, after expanding in the exhaust nozzle, to impart a thrust to the missile.

However. in order to obtain hypersonic (Mach 5 or above) flight speeds in ramjets, or to increase the efficiency of the ramjet at supersonic (Mach l to Mach 5) flight speeds, it is almost necessary to use a supersonic, rather than subsonic, combustion mode in the combustion chamber.

Dr. Antonio Ferri and his coworkers have developed the use of cryogenic hydrogen in supersonic combustion ramjets. It must be emphasized that these ramjets differ from the conventional ramjets discussed earlier in the use of a supersonic, rather than a subsonic, combustion mode.

Dr. Ferri and his coworkers have also tried to burn gaseous hydrocarbons such as methane and propane in such supersonic combustion ramjets. They have also tried to burn liquid hydrocarbons (by injection) in supersonic combustion ramjets. These efforts have been met with little, if any, success.

Thus, present technology considers liquid hydrogen as the only practical fuel for supersonic combustion ramjets. Thus far, pure hydrocarbons have not been considered suitable for supersonic combustion ramjets despite their suitability for subsonic combustion ramets.

J However. hydrogen suffers the disadvantage of being a cryogenic liquid and, therefore. not easily storable. Additionally. the heat of combustion of hydrogen on-a volume of liquid basis is poor.

Accordingly. it is an object of this invention to provide a new and improved storable liquid fuel for use in supersonic combustion ramjets.

A particular object of this invention is to provide a simple and effective scheme for vaporization and precombustor injection of suitable storable liquid fuels in supersonic combustion ramjets, such that storable liquids can be effectively and efficiently utilized for supersonic combustion.

A related object of this invention is to provide such fuels that have a heat of combustion greater than that of liquid hydrogen on a volume of liquid basis and are amenable to such a precombustor injection scheme.

SUMMARY OF THE INVENTION In accordance with this invention, a storable liquid propellant fuel is decomposed in flight into a hydrogencontaining gas which is injected into a supersonic airstream and then oxidized in a supersonic combustion mode. One method of accomplishing this is to simultaneously vaporize and convert liquid hydrazine, amine fuels, or blends of amines and hydrocarbons into a reactive hydrogen-containing gas by means of a prereactor employing thermal or catalytic decomposition beds,

prior to injecting the gas into the supersonic combustor. The hydrazine or amine type fuel must be exother- BRIEF DESCRIPTION OF THE DRAWING I These and other objects and advantages of this invention will become more readily apparent and understood by reference to the following detailed description, when considered in conjunction with the accompanying drawing, which forms an integral part thereof.

In the drawing:

FIG. 1 is a sectional view (shown schematically) of one embodiment of a ramjet of this invention; and

FIG. 2 is a sectional view (shown schematically) of another embodiment of a ramjet of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a portion of the outer shell 10 ofa ramjet engine 12 is shown. Shell 10 is a heavywalled metal tube and its bore forms a central duct or chamber 11, having a streamlined double-conical sleeve or supersonic diffuser 14 therein. Mounted inside supersonic diffuser 14 are a fuel tank 16, a gas generator 18 to the rear thereof, catalytic or thermal decomposition beds 23, injectors 20 for injecting fuel into catalytic or thermal decomposition beds 23, and porous plates or grids 25 on the outer ends of decomposition beds 23. Conduits 2] connect fuel tank 16 with decomposition beds 23 and contain valves 22 therein for controlling the flow of fuel to decomposition beds 23. Sleeve 14 forms an inlet section in the forward portion of chamber 11, a combustor section in the middle portion of chamber 11, and an exhaust section in the rear portion of chamber 11.

Inside fuel tank 16 is a storable hydrogen-containing liquid fuel, of the amine or hydrazine type or blends of amines with hydrocarbons, which is exothermally decomposing. The embodiment of FIG. 1, of course, is a monopropellant decomposition scheme. v

In the monopropellant decomposition scheme, decomposition beds 23 are of the catalytic or thermal type. An example of a catalytic decomposition bed will be found in Basic Factors Involved in the Design and Operation of Catalytic Monopropellant-Hydrazine Reaction Chambers," Report No. -77, A. F. Grant, Jr., Jet Propulsion Laboratory, California Institute ofTechnology. An example of a thermal decomposition bed will be found in Chemi-thermo Bed Techniques for Gas Generation, Dr. W. W. Wharton, J. W. Connaughton, Dr. J. A. Murfree, W. A. Duncan and B. .l. Sandlin, 3rd Joint Propulsion Specialists Conference of the AIAA, July, 1967.

In the operation of the monopropellant decomposition scheme of FIG. 1, the air for combustion enters the inlet section of chamber 11 and passes downstream through chamber 11, around supersonic diffuser 14 in the combustor section of ramjet l2, and out the ex haust section of ramjet 12.

Referring still to FIG. 1, a fuel such as NH NH is admitted from fuel tank 16 (after having been pressurized by gas generator 18) to injectors 20 (via conduits 21 and valves 22) and injected into the catalytic or thermal decomposition beds 23 where it is vaporized and decomposed into hydrogen-containing gases. It is then mixed with air passing through chamber 11 by being injected into the combustor section of the supersonic air stream through porous plates or grids 25. The resulting mixture is ignited, burned and exhausted out the exhaust section of chamber 11 to supply the propulsive force for the ramjet.

Referring now to FIG. 2, a portion of the outer shell 27 of a ramjet engine 29 is shown. Shell 27 is a heavywalled metal tube and its bore forms a central duct or chamber 28, having a streamlined double-conical sleeve or supersonic diffuser 31 therein. Mounted inside supersonic diffuser 31 are fuel tank 33, an oxidizer tank 40, a gas generator 32 to the rear of tanks 33 and 40, prereactors 39, injectors 35 for injecting fuel and oxidizer into prereactors 39, and porous plates or grids 41 on the outer ends of prereactors 39. Conduits 34 connect fuel tank 33 with prereactors 39 and contain valves 37 therein for controlling the flow of fuel to prereactors 39. Conduits 36 connect oxidizer tank 40 with prereactors 39 and contain valves 38 therein for controlling the flow of oxidizer to prereactors 39. Sleeve 31 forms an inlet section in the forward portion of chamber 28, a combustor section in the middle portion of chamber 28, and an exhaust section in the rear portion of chamber 28.

Inside fuel tank 33 is a storable hydrogen-containing liquid fuel, which is a hydrocarbon or hydronitrogencontaining compound. The embodiment of FIG. 2, of course, is a bipropellant decomposition scheme.

In the operation of the bipropellant decomposition scheme of FIG. 2, the air for combustion enters the inlet section of chamber 28 and passes downstream through chamber 28, around supersonic diffuser 31 in the combustor section of ramjet 29, and out the exhaust section of ramjet 29.

Referring still to FIG. 2, a liquid fuel such as unsymmetrical dimethylhydrazine is admitted from fuel tank 33 (after having been pressurized by gas generator 32) to injectors 35 (via valves 37 and conduits 34) and injected into prereactors 39 where it is vaporized and decomposed into a hydrogen-containing gas upon contact with oxidizer from oxidizer storage tank 40 (which is also pressurized by gas generator 32). Valves 37 and valves 38 are controlled by a single mechanism (not shown) which controls the combined flow of ozidizer (via valves 38 and conduits 36) and fuel in a preset oxidizer-fuel weight ratio. The hydrogen-containing gas which has been formed by the reaction between the fuel and oxidizer is then mixed with air passing through chamber 28 by being injected into the combustor section of the supersonic air stream through porous plates or grids 41. The resulting mixture is ignited, burned and exhausted out the exhaust section of chamber 28 to supply the propulsive force for the ramjet.

The storable fuel of the monopropellant decomposition scheme of FIG. 1 may be any exothermally decomposing liquid fuel of the amine or hydrazine type, or mixtures thereof, including mixtures with hydrocarbons.

Amines are nitrogen bases of the alkyl radicals. In other words, by the introduction of alkyl radicals in place of hydrogen into the ammonia molecule, the class of ammonia bases or amines is formed. The ammonia bases are divided into primary, secondary, tertiary and quaternary bases, according as they contain, 1, 2, 3 or 4 alkyl radicals; the first three are derived from ammonia, and the last from the hypothetical ammonium hydroxide, NH; OH. The lowest members of the amine class are gases. The next are liquids. The highest members of the class, such as triacetylamine, (C, H N, are at room temperature solid. The quaternary ammonium hydroxides are solid. The alkyl radicals in the amine may be either saturated or unsaturated. The term alkyl racical is defined herein to include monovalent radicals of both the aliphatic series, aromatic series and alicyclic series. The purely aliphatic alkyl radicals are termed alphyl groups, and the aromatic, aryl. Thus, aniline, a liquid, is a type of arylamine and may be viewed as ammonia in which a hydrogen is replaced by phenyl, C H Thus, it is included within the term amine, as defined herein. The arylamines are liquid or solid.

The amine may also be a mixed amine; e.g., an amine containing different alkyl groups in the molecule. Amines in which the NH group is attached to a carbon atom of a side chain, e.g., C H -CH -NH may also be used. In general, any amine may be used if it is an exothermally decomposing liquid.

The hydrazines are a series of peculiar bases, mostly liquid and closely resembling the amines, but containing two atoms of nitrogen in the molecule. They are derived from Diamide" or Hydrazine, NH NH Primary, secondary, tertiary and quaternary hydrazines are known, according as one, two, three or four of the hydrogen atoms in NH NH are replaced by alkyl groups. The secondary hydrazines exist in two isomeric forms, namely NHR'NHR and NH 'NR which are known respectively as symmetrical and unsymmetrical secondary hydrazines (R is an alkyl group). The terms hydrazines and amines are defined herein to include their derivatives and salts.

Examples of hydrazine compounds which have been found particularly satisfactory are unsymmetrical dimethylhydrazine and Diamide. In general, any exothermally decomposing liquid amine or liquid hydrazine, or mixtures thereof, may be used in the monopropellant decomposition scheme of FIG. 1. Preferably, the fuel should be rich in hydrogen.

In the bipropellant decomposition scheme of FIG. 2, the storable fuel may be, in general, any liquid hydrocarbon or liquid hydronitrogen-containing compound. Examples of hydronitrogen-containing compounds are hydrazines and amines, including those useful in the monopropellant decomposition scheme. Examples of liquid hydrocarbons are octane, heptane and JP-4 (a kerosene-base jet fuel). Of course, mixtures of such liquid fuels may also be used. Preferably, the fuel should be rich in hydrogen.

Just enough oxidizer must be mixed with the liquid fuel to produce sufficient heat to vaporize and crack the fuel into a hydrogen fuel-rich gas. An example which has proven satisfactory is an oxidizer to fuel weight ratio of 0.09 for inhibited red fuming nitric acid and unsymmetrical dimethylhydrazine.

The particular oxidizer chosen varies with the liquid fuel used and is well known to those skilled in the art. However, it should be easily storable. An excellent oxidizer is a mixture of N 0 and NO. The particular ratio chosen depends on storability requirements.

Other methods of converting the storable liquid fuel into a reactive hydrogen fuel-rich gas by means of a prereactor (prior to injecting the gas into the supersonic combustor) may also be employed.

Thus. this invention offers a simple way to use storable propellant fuels without the necessity of carrying liquid or gaseous hydrogen or maintaining a pilot flame for partial decomposition of such fuels to obtain hydrogen-containing gases. The ramjet engines of this invention may be employed in airplanes, missiles or the like.

Various other modifications and variations of this invention will become obvious to those skilled in the art in the light of the above teachings, which modifications and variations are within the spirit and scope of this'invention.

We claim:

l. The process of supersonic combustion of storable liquid propellant fuels comprising the steps of:

storing a liquid fuel in a supersonic diffuser of a supersonic combustion ramjet, said fuel being a hydrocarbon or a hydronitrogen-containing compound,

prereacting within said supersonic diffuser said liquid fuel by vaporizing and decomposing it into a hydrogen fuel-rich gas while said supersonic combustion ramjet is in flight, and

subsequently injecting said gas into a supersonic combustion air stream through said supersonic combustion ramjet while said supersonic combustion ramjet is in flight, thereby causing said gas and said air to react.

2. The process of claim 1 wherein said reacting is effected by catalytic decomposition means and wherein said liquid fuel is an exothermally decomposing hydrazine or amine.

3. The process of claim 1 wherein said prereacting is effected by thermal decomposition bed means and wherein said liquid fuel is an exothermally decomposing hydrazine or amine or blends thereof with hydrocarbons.

4. The process of claim 1 wherein said prereacting is effected by injecting a small amount of suitable storable oxidizer into said liquid fuel.

5. The process of claim 4 wherein said liquid fuel is unsymmetrical dimethylhydrazine, and wherein said storable oxidizer is inhibited red fuming nitric acid.

6. The process of claim 5 wherein the weight ratio of said inhibited red fuming nitric acid to said unsymmetrical dimethylhydrazine is about 0.09. 

2. The process of claim 1 wherein said reacting is effected by catalytic decomposition means and wherein said liquid fuel is an exothermally decomposing hydrazine or amine.
 3. The process of claim 1 wherein said prereacting is effected by thermal decomposition bed means and wherein said liquid fuel is an exothermally decomposing hydrazine or amine or blends thereof with hydrocarbons.
 4. The process of claim 1 wherein said prereacting is effected by injecting a small amount of suitable storable oxidizer into said liquid fuel.
 5. The process of claim 4 wherein said liquid fuel is unsymmetrical dimethylhydrazine, and wherein said storable oxidizer is inhibited red fuming nitric acid.
 6. The process of claim 5 wherein the weight ratio of said inhibited red fuming nitric acid to said unsymmetrical dimethylhydrazine is about 0.09. 